Photolithography is a technique for printing a pattern with features onto the surface of a substrate. A commonly-used substrate is a semiconductor wafer or a glass substrate which is surface-coated with a light-sensitive material. During a photolithography process, a wafer is placed on a wafer stage and the pattern with features is projected onto the surface thereof through an exposure device incorporated in the photolithography equipment.
Referring to FIG. 1, a conventional damping-free shutter device used in an exposure sub-system of a photolithography tool includes: at least two shutter blades 100 provided with respective voice coil motors 200 for driving the shutter blades 100 into an open or closed configuration. Motions of the shutter blades 100 toward the open or closed configuration as well as an extent to which they are opened or closed are controlled through adjusting currents flowing in mover coils of the voice coil motors 200. Referring to FIG. 4a, during operation of the damping-free shutter device, the mover coils in the voice coil motor 200 first accelerate for t/2 (i.e., 0-t1) under the effect of forward currents and then decelerate for t/2 (i.e., t1-t2) under the effect of reverse currents until their speeds decrease to zero. After the shutter blades 100 reach the open configuration, currents are further provided in order to keep them in the open configuration. In FIG. 4a, t1 denotes an instant of time when the conventional damping-free shutter device starts to be braked under the action of the reverse currents, t1-t2 indicates a period of time required for breaking of the conventional damping-free shutter device, Q represents a curve showing dependence of a Lorentz force acting on the mover coil in each of the conventional voice coil motors on time, and W indicates a curve illustrating evolution of an angle of deflection of each shutter blade 100 during its movement over time.
Therefore, the motions of the shutter blades 100 toward the open or closed configuration as well as the extent to which they are opened or closed are subject to an open-loop current control. The control side may interfere with the exposure process, and the open-loop current control may affect the stability of the shutter blades 100 during their acceleration and braking. Additionally, as the shutter blades 100 are separately controlled by the respective voice coil motors 200, there is a lack of consistency between their opening or closing processes, leading to insufficient repeatability of the shutter blade 100 and impaired exposure performance.